I was just reviewing an application that was obviously built upon a lot of the best practices advice for using an NHibernate application. I am currently in the process of ripping apart much of that application and then putting it back together again.
This involve things like collapsing projects, removing abstractions and deleting tests. The main reason for that is quite simple, the architecture is too big for the application. We can create a much more stream lined application is we don't burden it with an architecture that is suitable for bigger and more complex applications.
Selecting an inappropriate architecture is a big burden on an application, and it is one where you should be very careful. Chose an overly simplistic architecture, and you can only scale the application complexity with great difficulty. Chose an overly complex architecture, and you can't even get the baseline working easily, because of the complexity involved.
Don't try to make an application fit the architecture, and don't try to apply architecture blindly. Think and always start from the simplest thing that can possibly work.